Band Crossing and Novel Low-Energy Behaviour in a Mean Field Theory of a Three-Band Model on a Cu--O lattice

TL;DR

This paper explores a three-band Hubbard model for Cu--O planes, revealing band crossing phenomena near the Fermi level that influence low-energy behavior, Fermi surface nesting, and temperature-dependent relaxation rates.

Contribution

It introduces a mean field analysis of a three-band model showing band crossing effects and their impact on low-energy properties and optical conductivity.

Findings

Band crossing occurs near the Fermi level with increased oxygen orbital overlap.

Nearly nested Fermi surface leads to linear T dependence of quasiparticle relaxation.

Band crossing significantly affects optical conductivity and low-energy excitations.

Abstract

We study correlation effects in a three-band extended Hubbard model of Cu -- O planes within the 1/N mean field approach, in the infinite U limit. We investigate the emerging phase diagram and discuss the low energy scales associated with each region. With increasing direct overlap between oxygen orbitals, $t_{pp} >0$, the solution displays a band crossing which, for an extended range of parameters, lies close to the Fermi level. In turn this leads to the nearly nested character of the Fermi surface and the resulting linear temperature dependence of the quasi-particle relaxation rate for sufficiently large T. We also discuss the effect of band crossing on the optical conductivity and comment on the possible experimental relevance of our findings.